It has long been appreciated that the ability to adjust the brightness of the interior lights and panel/instrument displays is a desirable feature of an automotive vehicle. The use of a dimmer switch (typically a rheostat or variable resistor) on the dashboard is a commonly employed user interface for allowing control of the intensity of the light inside the vehicle. Pulse width modulation techniques have grown in popularity as the manner in which power is delivered to the lamps and other lighting devices such as electronic displays (e.g., a Vacuum Fluorescent Display (VFD)). Furthermore, the use of microprocessor based systems have become the dominant method of controlling most of the vehicle's systems, including the lighting system.
U.S. Pat. No. 4,358,713 illustrates a brightness control system in which a constant frequency oscillator circuit with a varying duty cycle is controlled by a variable resistor. The variable resistor is adjusted and set according to the brightness level desired by the operator/user. The output of the oscillator is fed to both filament lamps and a separate control circuit for the VFD. The separate control circuit produces a signal to the VFD which corresponds in frequency and duty cycle to that which is supplied to the filament lamps.
U.S. Pat. No. 4,968,917 illustrates a microprocessor based control system which uses a rheostat to adjust the brightness of the lighting devices. The direct current (DC) output of the rheostat drives the filament lamps of the interior of the vehicle. The same DC voltage is supplied to a VFD control circuit. A window of acceptable reference voltage levels is established around the DC voltage from the rheostat. The microprocessor initiates the generation of a series of discrete voltages whenever the rheostat DC voltage changes. Each discrete voltage initiated by the microprocessor is compared to the reference voltages of the window. When one of the microprocessor initiated discrete voltages falls within the window, a dimmer signal is sent to the VFD driver. The dimmer signal corresponds to the discrete voltage and it controls the duty cycle and consequent brightness of the VFD device.
In these, and other prior art systems, the maximum and minimum voltages possibly available from the system's dimmer switch are programmed, hardwired or hardcoded into a circuit or memory of the system. Since the predetermined maximum and minimum values have to take into account all possible production variations of the variable resistor (dimmer switch), any particular switch can reach its maximum or minimum voltage prior to the switch reaching the physical end of its travel.
It is one object of the invention to control the brightness of lighting devices within a vehicle.
It is one object of the invention to vary the brightness of lighting devices within a vehicle in response to the adjustment of dimmer switch.
It is further object of the invention to calibrate the variance of the brightness with respect to the physical travel limits of a variable resistor dimmer switch.